BPSC 71st CCE Prelims General Studies · Question 134 of 150

Correct — A, Platinum. The Commission, disposing of objections on 31 October 2025, gave its own reasoning: platinum-based compounds such as cisplatin, carboplatin and oxaliplatin are widely used against various carcinomas because they bind to the DNA of cancer cells, interfere with replication and lead to cell death — and it added that iron, by contrast, tends to promote cancerous growth. The founding drug is cisplatin, cis-diamminedichloroplatinum(II), cis-[Pt(NH₃)₂Cl₂], a square-planar platinum(II) coordination complex given as a short intravenous infusion in normal saline. Its mechanism is worth knowing precisely, because the chemistry is elegant. Outside the cell, where chloride sits near 100 mM, the two chloride ligands stay put. Inside the cell, where chloride is only about 3–20% of that concentration, one chloride is displaced by water — aquation — producing a reactive aqua complex. That species attacks the N7 nitrogen of guanine on DNA; displacement of the second chloride then locks the platinum to a neighbouring guanine. Roughly 90% of the resulting damage takes the form of 1,2-intrastrand cross-links between adjacent guanines, which kink the double helix, stall replication and mitosis, and when repair fails, trigger apoptosis. The drug has a datable history: first described by Michele Peyrone in 1845 as Peyrone's salt, with its structure deduced by Alfred Werner in 1893, then rediscovered biologically in 1965 when Barnett Rosenberg's group at Michigan State University found that platinum electrodes in a bacterial culture stopped E. coli dividing, leaving filaments up to 300 times normal length. It was approved by the US FDA on 19 December 1978 for testicular and ovarian cancer, and it is on the WHO Model List of Essential Medicines. Its clinical impact is the strongest evidence for the key: remission in testicular cancer rose from 5–10% before 1974 to 75–85% by 1984.

• (b)Chromium — Chromium is on the wrong side of the ledger entirely. Hexavalent chromium compounds are classified by the International Agency for Research on Cancer in Group 1 — carcinogenic to humans — on the evidence of lung cancer among chromate production, plating and pigment workers. Trivalent chromium is a trace element in the diet, but no chromium compound is an established anticancer therapy. The option tests whether you can tell a cause of cancer from a treatment for it.
• (c)Iron — The most tempting wrong answer, because school biology installs 'iron is good for you' very early — it is the metal at the centre of haemoglobin, myoglobin and the cytochromes, and its deficiency causes anaemia. But essential is not the same as therapeutic. Free iron drives Fenton chemistry, generating hydroxyl radicals that damage DNA, and iron overload is linked to raised cancer risk; the Commission made exactly this point in its published remark, that iron further induces cancerous growth.
• (d)Chlorine — Eliminated by the stem itself, which asks for a metal compound: chlorine is a halogen, a non-metal, a greenish-yellow gas used to disinfect water. The irony is what makes the option catch the eye of anyone who half-remembers the answer — chlorine really is inside cisplatin, as the two chloride ligands that are displaced when the drug activates. It is a genuine part of the right molecule, but it is not the metal that does the work.

Two ideas sit underneath this question. The first is what a carcinoma is. Cancers are named for the tissue they arise from: a carcinoma begins in epithelial tissue — skin, and the linings of the lung, breast, stomach, colon, cervix and other organs — while a sarcoma begins in connective tissue such as bone, muscle or cartilage, and leukaemias and lymphomas begin in blood-forming and lymphatic tissue. Carcinomas are by far the commonest group in adults, which is why a drug effective against them matters so much. The second idea is medicinal inorganic chemistry: the deliberate use of metal complexes as drugs. Cisplatin founded that field, and it remains its clearest demonstration that geometry, not merely composition, carries biological activity — transplatin, the trans isomer with the very same atoms, is essentially inactive, because its shape cannot form the characteristic cross-link between two adjacent guanines and it is deactivated before it reaches DNA. Cisplatin is also the standard illustration of a drug limited by its side effects: kidney damage is the dose-limiting toxicity, with nerve damage, hearing loss and severe nausea alongside it, which is why carboplatin and oxaliplatin were developed as better-tolerated successors. Metals appear elsewhere in the pharmacy too — lithium carbonate in bipolar disorder, gold compounds in rheumatoid arthritis, silver sulfadiazine on burns, gadolinium as an MRI contrast agent, technetium-99m in nuclear imaging, arsenic trioxide in one form of leukaemia — but platinum is the only metal at the centre of mainstream cytotoxic chemotherapy.

The stem does half the work if you read it carefully: it asks for a metal compound. Chlorine is a non-metal, so option (d) falls in one second — and it is precisely the option a hurried candidate might tick, because chloride genuinely appears in cisplatin. Reading the stem beats recognising a fragment. That leaves three metals, and the next filter is whether each is famous for causing cancer or for treating it. Hexavalent chromium is a recognised human carcinogen, so (b) is on the wrong side. Iron is essential to life but is not a therapy, and in excess it promotes rather than prevents malignant growth — the point the Commission made explicitly when it upheld this key. Only platinum is famous as a treatment, and the single discriminating fact is that the platinum drugs — cisplatin, carboplatin, oxaliplatin — are the only metal-based cytotoxic agents in routine oncology anywhere in the world. The trap is (c) iron, and it is well chosen, because the association between iron and health is one of the strongest a student carries out of school. The habit worth building is to separate three categories that examiners deliberately blur: an essential nutrient (iron, zinc, copper), an occupational carcinogen (chromium(VI), nickel, asbestos), and a therapeutic agent (platinum complexes). A metal can sit in any one of them, and belonging to the first says nothing about the third.

• Cisplatin is cis-diamminedichloroplatinum(II), cis-[Pt(NH₃)₂Cl₂], a square-planar platinum(II) complex given by intravenous infusion. It was approved by the US FDA on 19 December 1978 for testicular and ovarian cancer and appears on the WHO Model List of Essential Medicines.
• Mechanism: inside the cell, where chloride is only about 3–20% of the roughly 100 mM level outside, one chloride is replaced by water; the resulting complex binds the N7 of guanine and then cross-links to a second guanine. About 90% of the adducts are 1,2-intrastrand links between adjacent guanines, which block replication and mitosis and trigger apoptosis.
• Geometry decides activity: transplatin, the trans isomer with identical atoms, is essentially inactive because it cannot form the 1,2-intrastrand cross-link and is deactivated before reaching DNA. Cisplatin was first described by Michele Peyrone in 1845 and its structure deduced by Alfred Werner in 1893.
• The anticancer effect was found by accident in 1965, when Barnett Rosenberg's group at Michigan State University saw that a platinum complex released from electrodes stopped E. coli dividing — the cells kept growing into filaments up to 300 times their normal length.
• Cisplatin transformed testicular cancer, where remission rates rose from 5–10% before 1974 to 75–85% by 1984. Its dose-limiting toxicity is kidney damage, with nerve and hearing damage and severe nausea also common, which is why the later platinum drugs carboplatin and oxaliplatin were developed.

• Choosing iron because it is essential to health — an essential nutrient is not a therapy, and iron in excess promotes rather than checks malignant growth
• Choosing chlorine because chloride ligands really are part of cisplatin — the stem asks for a metal, and chlorine is a non-metal
• Confusing a carcinogen with a cure: chromium(VI) causes occupational lung cancer, it does not treat it

BPSC asks it as a single-word identification with an applied hook — which metal treats cancer — and then, unusually, published the mechanism itself in its remarks, down to the point that iron works the other way. UPSC has never asked for a chemotherapy drug by name; it approaches cancer through the modality or the biology instead, asking why cobalt-60 suits radiation therapy in 1999, what a cyberknife can and cannot do in 2010, and what metastasis means in 2001. Expect BPSC to want the substance and UPSC to want the process.

• practice — not a real PYQ

  Cisplatin, a widely used anticancer drug, exerts its effect mainly by

  • (a)Binding to and cross-linking the DNA of dividing cells, blocking replication
  • (b)Blocking the action of the enzyme acetylcholinesterase
  • (c)Neutralising the acid produced in the stomach
  • (d)Stimulating the production of red blood cells in bone marrow

  Answer(a) Binding to and cross-linking the DNA of dividing cells, blocking replication — the platinum binds mainly at the N7 of guanine and forms 1,2-intrastrand cross-links that stall replication and mitosis and end in apoptosis.

• practice — not a real PYQ

  Which one of the following metals is classified as a human carcinogen in its hexavalent form rather than being used to treat cancer ?

  • (a)Platinum
  • (b)Chromium
  • (c)Magnesium
  • (d)Sodium

  Answer(b) Chromium — hexavalent chromium compounds are classified as carcinogenic to humans, with lung cancer documented among chromate and plating workers. Platinum complexes are the therapy; magnesium and sodium are ordinary physiological electrolytes.